The present invention relates generally to an ink jet recording apparatus and, in particular, to an ink jet recording apparatus which ejects ink directly onto a recording medium for forming characters thereon and which prevents problems caused by air bubbles in the ink and clogging of the ink passages.
Many types and constructions of ink jet recording devices have been developed and utilized heretofore. One such ink jet recording apparatus which selectively ejects ink only on demand is described in Japanese Laid-Open Patent Publication No. 51-35231 and should receive attention because of the simplicity of its construction. The ink jet recording apparatus of this type has gone through many improvements and modifications, but has not been rendered practically feasible due to lack of reliability. Those devices which have been available for practical use suffer from limitations such as the ease of use, and have therefore proven unsatisfactory.
The difficulty arises because of the fact that no final solutions have been found to the problems caused by air bubbles in the ink and the problems caused by clogging of the ink passages. As can be understood from the principles of recording described in the aforementioned Japanese Publication No. 51-35231, no ink can properly be ejected when air bubbles are trapped in a pressurization chamber for pressurizing ink on the ink jet head. Ink passage clogging happens not only in the ink jet recording apparatus under consideration, but also in all forms of ink jet recording devices. However, this clogging problem is even more pronounced particularly with the ink jet recording apparatus of the ink-on-demand type as the ejection nozzle thereof has a relatively small cross section.
Various proposals to solve the problems encountered in ink jet recording will be described herein. There have been suggested many improved ways of removing air bubbles from the ink that tend to be included in the ink such as when the ink is initially loaded in the device or a cartridge of ink is replaced. Representative are a device for removing air bubbles through ink circulation such as is disclosed in Japanese Laid-Open Patent Publication Nos. 54-159227 and 54-160242, for example, and an air bubble remover disposed in a passage of the ink such as is described in Japanese Laid-Open Patent Publication No. 51-88224. Although means are disclosed in Japanese Patent Publication No. 53-20882 for removing air bubbles which are formed within ink due primarily to cavitation, substantially no consideration has been given to coping with such air bubbles when they remain in the ink. Attempts to prevent an ink passage in the apparatus from becoming clogged include providing improved ink compositions, providing a cover for an ejection nozzle in the ink jet head, and providing means for forcibly releasing the ink passage of clogging, for example, as described in Japanese Laid-Open Utility Model Publication No. 54-66853. However, these attempted arrangements have proven unsatisfactory for the reasons described hereinafter. Accordingly, an improved ink jet recording apparatus which is reliable in operation and which avoids the problems encountered in the prior art devices such as those caused by air bubbles and clogging is urgently desired.